1. Field of the Invention
This invention generally relates to a torque converter. More specifically, the present invention relates to a torque converter having a lockup device.
2. Background Information
In general, a torque converter can smoothly accelerate and decelerate because power is transmitted by fluid. However, a loss of energy can be caused by fluid slip resulting in poor fuel economy. Therefore, a torque converter that is mounted with a lockup device for mechanically connecting an input-side front cover and an output-side turbine exists among prior art torque converters. The lockup device is disposed in a space between the front cover and the turbine. The lockup device is mainly formed of a disc-shaped piston, a driven plate, and a torsion spring. The disc-shaped piston can be pressed against the front cover. The driven plate is mounted to a back face side of the turbine. The torsion spring elastically connects the piston and the driven plate in a rotating direction. An annular frictional member is arranged on the piston and faces a flat frictional face of the front cover.
In a conventional prior-art lockup device, actuation of the piston is controlled by change in hydraulic pressure in a fluid chamber. Hydraulic fluid is preferably supplied between the piston and the front cover from an outside hydraulic circuit when the lockup device is disconnected. This hydraulic fluid flows radially outward through a space between the front cover and the piston and flows into a torque converter main body on an outer periphery portion side. In a lockup connection, the hydraulic fluid in a space between the front cover and the piston is drained from an inner periphery side. As a result, the piston moves toward a front cover due to a hydraulic pressure difference. The frictional member provided on the piston is pushed against the frictional face of the front cover. Thus, torque from the front cover is transmitted to a turbine side through the lockup device.
On the other hand, improved performance of a damper mechanism is desired between low speeds of a vehicle and increases in torque. In recent years, there is a known torque converter in which torque is transmitted by fluid only when a vehicle starts, and the lockup device is connected at a speeds of 20 km per hour or greater, for example. In such a structure in which a lockup region is expanded, improved performance of the torsion spring is desired to absorb and damp torsional vibrations sufficiently in response to torque changes from an engine. Improving vibration absorbing/damping characteristics for torsional vibration by increasing a diameter of the torsion spring is desired. However, since the torsion spring is disposed axially between the front cover and the turbine, the size of the entire torque converter increases if the torsion spring size is increased.
In view of the above, there exists a need for torque converter that overcomes the above-mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
It is an object of the present invention to improve performance of a torsion spring, preferably through increasing its size, while suppressing an increase of an axial dimension of a torque converter in the torque converter provided with a lockup device.
A torque converter according to a first aspect of the present invention has a toric fluid actuating portion that includes an impeller, a turbine, and a stator. A ratio (D2/D1) of an inside diameter D2 to an outside diameter D1 of the fluid actuating portion is equal to or greater than 0.61. In this torque converter, since the inside diameter of the fluid actuating portion is larger than that of the prior art, it is possible to dispose the torsion spring of the lockup device on an inner periphery side of the fluid actuating portion. Therefore, it is possible to increase sufficiently the size of the torsion spring to improve performance of the torsion spring without increasing the axial dimensions of the torque converter.
In a torque converter according to a second aspect of the present invention, the torque converter of the first aspect has a ratio in which the D2/D1 is in a range of 0.61 to 0.77. If D2/D1 becomes equal to or greater than 0.77, a flow path area in the torus becomes very small and therefore a flow rate acting on blades decreases. Thus, a torque capacity of the impeller becomes small. Moreover, a radius of an outlet of the turbine becomes large and the maximum efficiency of the torque converter is reduced.
A torque converter according to a third aspect of the present invention has a front cover, a fluid actuating portion, and a lockup device. The fluid actuating portion includes an impeller, a turbine, and a stator connected to the front cover. The lockup device is disposed between the front cover and the turbine to connect mechanically both the front cover and turbine. The lockup device has a torsion spring for absorbing and damping torsional vibration. An outer peripheral edge of the torsion spring is positioned on an inner periphery side of an inner peripheral edge of the fluid actuating portion.
In this torque converter, the torsion spring of the lockup device is not arranged side by side with the fluid actuating portion in an axial direction but positioned on a radially inner side of the fluid actuating portion. Therefore, it is possible to increase sufficiently the size of the torsion spring to improve performance of the torsion spring without increasing the axial dimension of the torque converter.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses a preferred embodiment of the present invention.